Superman (gene)

Superman is a plant gene in Arabidopsis thaliana, that plays a role in controlling the boundary between stamen and carpel development in a flower.[1] It is named for the comic book character Superman, and the related genes kryptonite (gene) and clark kent were named accordingly (although the latter turns out to just be another form of superman).[2] It encodes a transcription factor (specifically a C2H2 type zinc finger protein).[3] Homologous genes are known in the petunia[4] and snapdragon,[5] which are also involved in flower development, although in both cases there are important differences from the functioning in Arabidopsis. Superman is expressed early on in flower development, in the stamen whorl adjacent to the carpel whorl.[4] It interacts with the other genes of the ABC model of flower development in a variety of ways.[4]

Gene function

Superman encodes a transcription factor.[3] This protein binds to the DNA through a zinc finger binding motif[3] acts as a regulator of floral homeotic genes, controlling the development of the flowers of Arabidopsis thaliana plants. Arabidopsis thaliana flowers develop in four whorls, which are concentric groups of cells branching off of the growing meristem.[6] Superman has been found to act in the fourth whorl of flowers, which would normally develop into Carpels. Superman normally restricts the effect of another gene called (APETALA3) in the fourth whorl, leaving APETALA3 expression only present in the second and third whorls.[6] APETALA3 is a gene normally associated with the development of a stamen in the third whorl,[7] so by its restriction, we allow for the development of other organs in the fourth whorl (such as the Pistil).

A mutation which completely removes superman gene function would result in flowers that carry extra stamens, replacing the pistils which would normally be developing in the fourth whorl. This mutation was named the sup-1 mutation. For the sup-1 mutation, More extreme stamen development is seen from a homozygous mutation than a heterozygous mutation.[8]

Interaction with the ABC model of flower development

The gene which Superman interacts with (APETALA3) is a member of the B-Function group of the ABC model of flower development,[7] which is typically responsible for the development of Stamen and Petals. Other important members of the ABC model of flower development include APETALA1, APETALA2, AGAMOUS, and PISTILATA.[9] Superman has not been found to interact with any of these other genes.

Epigenetic changes to Superman

Superman has been found to undergo to epigenetic modifications. Specifically, cytosine methylation (attachment of methyl radicals to cytosine bases), which represses its transcriptional activity. This methylation brings about the Clark Kent (clk) epialleles, which are a set of altered versions of the Superman gene lacking function.[10] Whereas most cases of cytosine methylation in plants tend to happen in the Promoter of transcription, the cytosine methylation of Superman happens within the gene, just after the promoter.[6] The exact location of the methylation varies, but defines which clk epiallele we define the plant as having; so far there are 7 identified clk epialleles (numbered clk1-clk7).[10]

These Clark Kent alleles can be inherited, but often, through mutation will revert to the natural gene at a rate of about 3% per generation[11]

References

  1. ↑ "Gene Model: SUP". The Arabidopsis Information Resource (TAIR). 2006-02-01. Retrieved 2007-01-23.
  2. ↑ "Clever Arabidopsis gene names". Clever gene names. Mikael Niku and Mikko Taipale. 2005-12-03. Retrieved 2007-01-23.
  3. 1 2 3 Jae-Young Yun, Detlef Weigel & Ilha Lee (2002). "Ectopic Expression of SUPERMAN Suppresses Development of Petals and Stamens". Plant and Cell Physiology. 43 (1): 52–57. doi:10.1093/pcp/pcf018. PMID 11828022.
  4. 1 2 3 Hitoshi Nakagawa; Silvia Ferrario; Gerco C. Angenent; Akira Kobayashi & Hiroshi Takatsuji (April 2004). "The Petunia Ortholog of Arabidopsis SUPERMAN Plays a Distinct Role in Floral Organ Morphogenesis". Plant Cell. 16 (4): 920–932. doi:10.1105/tpc.018838. PMC 412866Freely accessible. PMID 15020746.
  5. ↑ Box 3: The control of floral determinacy in Antirrhinum and Arabidopsis from Zsuzsanna Schwarz-Sommer, Brendan Davies & Andrew Hudson (August 2003). "An everlasting pioneer: the story of Antirrhinum research". Nature Reviews Genetics. 4 (8): 655–664. doi:10.1038/nrg1127. PMID 12897777.
  6. 1 2 3 Chan, Simon W.-L.; Henderson, Ian R.; Jacobsen, Steven E. (2005-05-01). "Gardening the genome: DNA methylation in Arabidopsis thaliana". Nature Reviews Genetics. 6 (5): 351–360. doi:10.1038/nrg1601. ISSN 1471-0056.
  7. 1 2 Krizek, B. A.; Meyerowitz, E. M. (1996-01-01). "The Arabidopsis homeotic genes APETALA3 and PISTILLATA are sufficient to provide the B class organ identity function". Development (Cambridge, England). 122 (1): 11–22. ISSN 0950-1991. PMID 8565821.
  8. ↑ Bowman, John (1992). "SUPERMAN, a regulator of floral homeotic genes in Arabadopsis" (PDF). Development.
  9. ↑ Bowman, John L.; Smyth, David R.; Meyerowitz, Elliot M. (2012-11-15). "The ABC model of flower development: then and now". Development. 139 (22): 4095–4098. doi:10.1242/dev.083972. ISSN 0950-1991. PMID 23093420.
  10. 1 2 Jacobsen, Steven E.; Meyerowitz, Elliot M. (1997-08-22). "Hypermethylated SUPERMAN Epigenetic Alleles in Arabidopsis". Science. 277 (5329): 1100–1103. doi:10.1126/science.277.5329.1100. ISSN 0036-8075. PMID 9262479.
  11. ↑ Kakutani, Tetsuji (2002-10-15). "Epi-Alleles in Plants: Inheritance of Epigenetic Information over Generations". Plant and Cell Physiology. 43 (10): 1106–1111. doi:10.1093/pcp/pcf131. ISSN 0032-0781. PMID 12407189.
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